1. Field of the Invention
This invention relates generally to a bipolar transient driver circuit and, more particularly, to a monolithically integrated AC bipolar transient driver for quickly charging and discharging a large capacitance while maintaining a low power requirement.
2. Background Art
A number of circuits exist that inherently have a relative large capacitance appearing at their input terminal. For example, the capacitive metal interconnects of a gate array present input signal transition difficulties. Also, the capacitance within a memory cell slows down its response to an input signal.
One known transition circuit comprises an NPN transistor coupled between supply voltage V.sub.CC and an output terminal (the input terminal of the capacitive circuit) and responsive to an input signal for driving the capacitive circuit positive. An NPN discharge transistor has a collector connected to the output terminal of the transition circuit and an emitter coupled to supply voltage V.sub.EE by a resistor. However, in order to discharge the capacitance quickly, the resistance must be small. This results in an undesirably large current.
Another known transition circuit, for increasing the downward transition of a memory cell, comprises an NPN transistor responsive to a select signal and coupled to a select line for providing current to a plurality of memory cells. A first PNP transistor has a collector coupled to supply voltage V.sub.EE and an emitter coupled to a current drain line for drawing any charge from the plurality of memory cells when the select signal transitions downward. Means are coupled to the base of the first PNP transistor and are responsive to the select signal for setting the current level in the first PNP transistor. A second PNP transistor has an emitter coupled to the select line and a collector coupled to supply voltage V.sub.EE for removing charge stored on the select line. The second PNP transistor has its collector isolated from the substrate, limiting circuit high frequency operation. Also, emitter-base forward voltage mismatch occurs between the isolated and non-isolated devices.
Thus, what is needed is an improved AC bipolar transient driver circuit that charges and discharges a large capacitance at its output terminal quickly and with low current requirements.